The invention relates to a recording medium discharge mechanism for use in printers.
A conventional recording sheet discharge mechanism for printers will be described with reference to FIGS. 5 and 6(a)-6(c). FIG. 5 is a sectional view showing a recording sheet discharge mechanism. A recording sheet S, which has already been printed by a recording head 82, is interposed under pressure between a sheet discharge roller 69 and a sheet discharge biasing roller 72 which are disposed at the front end of a sheet discharge tray 14. The recording sheet S is discharged into the sheet discharge tray 14 by rotating the sheet discharge roller 69 in a direction indicated by the arrow in FIG. 5 from a torque transmitted by a drive means (not shown).
FIG. 6(a) shows the profile of the sheet as discharge rollers 69 including a plurality of rectangular teeth disposed on the outer peripheral surface thereof. Further, as shown in FIG. 6(b), the sheet discharge biasing rollers 72 are disposed so as to be slightly staggered relative to the sheet discharge rollers 69 in the axial direction of the rollers and to be slightly superimposed one upon the other in the radial direction. The printed recording sheet S is interposed between the sheet discharge rollers 69 and the sheet discharge bias rollers 72 so as to form a large wave extending in the width-wise direction of the sheet, as illustrated, causing the sheet to be relatively rigid. The sheet discharge rollers 69 are rotated by a drive means (not shown) such that the recording sheet S is forwarded and discharged. When feeding and discharging the recording sheet S into the sheet discharge tray 14, as shown in FIG. 6(c), as its tail end reaches the sheet discharge rollers 69, the toothed portion formed on the peripheral surface of each sheet discharge roller 69 urges the recording sheet S into the sheet discharge tray 14.
However, the conventional device has experienced the following problems. When printing with an ink jet printer, which prints a recording object while spraying ink droplets onto a recording medium, a printed portion on the recording sheet is still wet when the recording sheet is to be discharged. Since the sheet discharge mechanism shown in FIG. 6 causes the printed recording sheet to be clamped between the sheet discharge roller and the sheet discharge biasing roller, the printed object becomes smeared. Further, since the recording sheet is no longer fed after its tail end passes the area at which it is held between the sheet discharge roller 69 and the sheet discharge biasing roller 72, conveyance of a succeeding recording sheet is obstructed by the tail end of the preceding recording sheet which is still disposed near the sheet discharge roller 69, thus leading to jamming of the sheets.
On the other hand, to discharge a recording sheet which is not curled while using the sheet discharge mechanism shown in FIGS. 6(a)-6(c), the toothed portion pushes the tail end of the recording sheet, thereby allowing the recording sheet to be discharged into the sheet discharge tray. However, if the tail end of the recording sheet is noticeably curled prior to printing, and if the ink jet printer is used, the curl of the tail end of the sheet may become more pronounced. As a result, the tail end of the sheet may be curled to such a degree that the tail end does not contact the toothed groove portion of the sheet discharge roller. In this case, the recording sheet will not be completely discharged by the sheet discharge roller into the sheet discharge tray. Accordingly, a succeeding recording sheet may become jammed by the tail end of the preceding sheet still present on the sheet discharge roller.